Typically in a design of such nature their are more then one lighting circuit in each area. For example one or two circuits from the emergency pane and others from the regular panel. Many designs of large areas have "nights lights" that are on 24/7. In the concept Scott35 is proposing, the NL's which double as emergency lights and exits would be on the generator panel and the other areas would be in other panels. The likelyhood is slim that both circuits in the same area and the same time would fail. Someone would notice if the emergency circuit had failed if wired in this manner.
And of course the AHJ must be on board with it.
You could even switch the NL's providing they were wired in a manner where if the generator would fire, it would energize a contactor that would by-pass the switch legs. It is not cheap but on the size of facility Scott35 is working on, that could finacial incentive that can be determined with some cost analysis to see the savings would offset the cost. The cost which is basically the cost of the contactor and parallel run of wire with each e-lighting circuit. In a sense it would like placing a three way switch (the contactor) under supervised control (to meet NEC 700) and switching the only one of "travelers" at the load end.
You could even wire it that if the coil or control circuit failed on the contactor, fail safe mode would engage the e-light circuits. It would be noticed and it could be fixed.
